Sorry no time to edit this down!
Little silica gel bags wont do much in a cardboard hanging wardrobe. It's just a tall box at the end of the day. Put them into the bottom of sealed garment bags, maybe.
IME chosing the right place, then 'shrouding' quality clothes in acid free paper, and placing in good quality zip up garment bags, is your best bet if you want to store them hanging for a year, in a standard metal walled storage unit.
An awful lot can happen in a storage unit in a year, and conversely nothing can happen. including both case scenarios in the same building with different units.
You have other threads mentioning 'good coats' and 'designer' bags, as well as worry.
A lot of the answers depend on where you're storing and is it an old building converted, or purpose built. (They both have different issues, but some never affect the majority of users.)
The later are very common - purpose built storage units at roof level is a bad idea for a year, they nearly all have effectively metal roofs and get very hot in summer and very cold in winter. Below ground level depends on how water tight the building actually is, many are very damp hidden behind shiny metal walls, many develop damp as a result of what's going on next to them. (building, road works etc.)
Converted buildings often have a nasty tendency to have incoming water issues, leaks, pipes, roofs, floods.
Rodents are common in both. They walk* and burrow in, and people illicitly store things they eat. Some places develop serious clothes moth infestations. Use your eyes, and don't just look at the unit you're being offered, check out the building.
Ground floor units are at a premium, and often have *higher rodent issues.
Take nothing with a pipe running through it. (even when they swear blind it's disused.) There's a reason it's discounted.
For a years storage you want a unit bang in the middle of the building.
Once in, leave a gap at the sides for air flow. (and if you want to get serious; use pallets to create an air vent underneath) If using cardboard boxes: use shelving to reduce stacking, rather than stacking floor to ceiling. Heavy at bottom, light on top.
All companies reserve the right to move you to a different unit if they 'need' to. Their concept of 'need' is generally whatever works best for their business.
If you're not there to do the move, it will be done for you. That fabulous manager you trusted has often gone elsewhere in four months. The ethos of a place can change quickly. Your careful stacking may not be adhered to. ('It's what insurance is for' is the argument)
Companies are brought out by bigger companies and the rules and conditions changed underneath you, including what you are allowed to store. (or is covered by insurance)
If you're leaving it for a year (especially if not visiting) prep your goods that truly matter, for worst case scenario's, and hope for best case. If you're going abroad etc, have a contingency plan. You probably wont need it, but if you do, you'll be so glad you figured out here.
Most cardboard boxes, including hanging wardrobes, use glue that is food to beetles and moths. Hanging wardrobe for a year without further protection is a total gamble. You may be perfectly fine, you may not be.
Most cardboard used in boxes contain acids.
This stuff only gets really important when talking about preservation, and longer term storage with certain materials, but includes stuff like vintage Christmas decorations, some metal fasteners and decoration on expensive bags, belts etc, metal thread embroidery, silk embroidery, art, some books, etc.
Acid free tissue paper and acid free brown paper are your friends there, and worth spending on and layering if you're trying to look after specific items.
Unless very deeply wrapped, don't then use standard tape, string or plastic ties on them. (don't buy supposed cheap acid free tissue from China, it rarely is.)
Thoroughly clean all materials before storage. If dry cleaning hang for at least 72 hours afterwards if packing up.
Standard stuff like bedding, towels etc, use vacuum bags, doesn't have to loose all the air, and rolling instead of folding, will ensure no deep creasing. But you can also use standard poly bags, inside cardboard boxes. Double bag if worried about moths.
Wool and silk need to breathe (I know nothing about leather) but are favored material for clothes moths so it's always a balance.
Proper cedar wood will deter clothes moths so if you are talking something seriously 'good' or entirely irreplaceable, vintage etc, then cedar wood boxes are the ultimate bug protection, not cheap, but hold good resale value. Pick the right ones, and they actually increase in value.
There are acid free plastic storage boxes with vents, which are excellent, but they're expensive and not much of a resale market, because mainly brought by professional institutions, as new.
Really Useful Boxes are expensive, but do the job properly, and have a good resale market as highly durable and recognized by lots of different sectors as worth snapping up.
Standard plastic boxes degrade quite quickly, so tend not to do as well for resale, but you can get lucky, especially if you stick to known brands.